The magnetic resonance imaging (MRI) system in clinical is categorized according to the type of the magnet (e.g., permanent magnet, superconducting magnet). The superconducting magnet has high magnetic field intensity (usually 1.5 or 3 Tesla). The superconducting magnet may attract ferromagnetic materials nearby, and the attracted ferromagnetic material can be taken down only after the superconducting magnet is ramped down (e.g., by ramping down the superconducting magnet). According to some regulations and laws, a ramping-down switch (or ramping-down circuit) is required to ramp down the superconducting magnet in an emergency. When metal tools, a patient with a metal implant or heart pacemaker close to the MRI system, the superconducting magnet may be ramped down in a short time (usually 20 seconds) by turning on the ramping-down switch.
When turning on the ramping-down switch, a heater may heat a superconducting coil, then the superconducting coil may be ramped down and reverts to a resistive state, and the electric current flowing through the resistive part of the superconducting coil may be consumed in about 20 seconds and converted into a large amount of Joule heat. The superconducting coil may usually be soaked in liquid helium in a cryogenic container. The Joule heat would lead to the bulk of liquid helium volatilized. After superconducting magnet is ramped down, the liquid helium need to be added to convert the superconducting magnet into superconducting state, and adding the liquid helium would bring huge cost.